Dressings with a foamed adhesive layer

ABSTRACT

A dressing suitable for topical application to the body, including a carrier substrate having a first side and opposing second side; and a layer of a foamed adhesive composition applied to the second side of the carrier substrate, where the layer of foamed adhesive composition includes a substantially homogeneous distribution of closed cells having an inert gas contained therein.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application claiming thebenefit of the earlier filing date of U.S. patent application Ser. No.13/246,921, filed Sep. 28, 2011, the entirety of which application ishereby incorporated by reference herein as if fully set forth herein.

FIELD OF THE INVENTION

This invention relates to a dressing for topical application to the bodyand that includes a carrier substrate and foamed adhesive layer appliedto the carrier substrate, where the foamed adhesive layer includes aplurality of closed cells that include an inert gas disposed therein andwhich are substantially homogeneously distributed throughout the foamedadhesive layer.

BACKGROUND OF THE INVENTION

Adhesives for dressings that may be placed in contact with skin, eitherdirectly or indirectly, are known in the art. Such dressings includeadhesive bandages for direct application to wounds in the skin, as wellas absorbent articles, such as sanitary napkins, that are indirectlyplaced in contact with the skin via attachment to undergarments orarticles of clothing. Such adhesives include hot melt adhesives.

Hot melt adhesives are applied to carrier substrates in molten form andtypically will form a solid layer on the substrate upon cooling. Suchadhesive compositions and layers typically will be substantially void ofbubbles or pores that may contain air or other gases. Other hot meltadhesives, such as those described in U.S. Pat. No. 6,383,630, mayinclude open cells or pores, and form open-celled adhesive layers whichare said to exhibit good permeability to air and water vapor. Asdescribed therein, the adhesive composition is “applied not to theentire area of at least one side” of the carrier substrate. The adhesivelayer preferably is preferably patterned in a dome form. The adhesivelayers in dressings exemplified therein are applied to the carriersubstrate by thermal screen printing.

Dressings of the present invention permit reduction of the amount ofadhesive composition that must be applied to the carrier substrate, thusresulting in cost savings versus dressings that use a substantiallysimilar non-foamed adhesive composition, while maintaining adhesion andbulk properties necessary for use in such dressings.

SUMMARY OF THE INVENTION

The invention relates to a dressing suitable for topical application tothe body, the dressing including a carrier substrate having a first sideand an opposing second side; and a layer of a foamed adhesivecomposition applied to the second side of the carrier substrate. Thelayer of foamed adhesive composition comprises a substantiallyhomogeneous distribution of closed cells comprising an inert gascontained therein.

DETAILED DESCRIPTION

The invention relates to dressings that are topically applied to orotherwise placed in contact with the body for use in variousapplications. Dressings according to the invention include, withoutlimitation, adhesive bandages for use in wound care, e.g. forapplication to cuts and scrapes in the skin, and feminine sanitaryprotection products, e.g. napkins and liners. Such dressings willinclude a carrier substrate having at least one side to which a foamedadhesive composition as described herein is applied to form an adhesivelayer for the purpose of securing the dressing in place relative to thebody. The adhesive layer will contain a proportion of inert gascontained in a plurality of closed cells, which cells are substantiallyhomogenously distributed throughout the adhesive layer.

Foamed adhesive compositions which can be employed in dressings of thepresent invention may be hot-melt adhesives having a plurality of closedcells that contain an inert gas disposed therein and which aresubstantially homogenously dispersed throughout the adhesive. By“substantially homogenously dispersed”, it is meant that the number andvolume of closed cells dispersed in any portion, e.g. volume, of thefoamed adhesive composition or foamed adhesive layer is approximatelythe same. By “closed cell”, it is meant that the cells are predominantlyisolated from one another and are bounded by a definite/intact cellboundary of continuous adhesive material, i.e. a substantiallycontinuous cell wall, such that the inert gas is encapsulated andretained within the cells.

The closed cells in the foamed adhesive composition may have an ovoid,spherical or circular structure. The closed cell in the foamed adhesivetypically will have a maximum cell dimension, e.g. maximum average celldiameter, of about 10 micron, or about 5 micron. The cell dimension mayrange from about 1 to about 10 micron, or from about 2 to about 5micron, depending on the particular application. While it is possiblefor the foamed adhesive compositions to include some relatively minorlevel of open cells, the cell volume in the adhesive composition ispredominately made up of closed cells. Typically, the total number ofcells in the adhesive composition and/or the adhesive layer will containless than 10% of open cells, and will comprise about 90% or more ofclosed cells, and even more typically will comprise about 95% or more ofclosed cells.

The cell boundary prevents the free flow of inert gas from the closedcell in the foamed adhesive, allowing only minimal permeation.Furthermore, due to the closed cell structure, the inert gas will noteasily escape from the closed cells upon application of pressureassociated with applying the dressing to the carrier substrate. Inaddition, the closed-cell nature of the foamed adhesive provides for ahighly effective air barrier, low moisture vapor permeability andexcellent resistance to water.

The foamed adhesive compositions used in the present invention may bebased on materials that are used to prepare adhesives used inconventional dressings, including without limitation, natural and/orsynthetic rubbers and/or on other synthetic polymers, such as acrylates,methacrylates, polyurethanes, polyolefins, polyvinyl derivatives,polyesters or silicones, or blends thereof. The adhesive compositionsmay also include appropriate additives, such as adhesion resins,plasticizers, stabilizers and other auxiliary components where necessaryor desired.

Gases used to prepare adhesive compositions utilized in the presentinvention may be inert gases selected from the group consisting ofnitrogen, carbon dioxide, noble gases, hydrocarbons; and air. In thecase of air, anti-oxidants may be added to the adhesives. Because of theinert nature of the gases, there are no reactions between the adhesivecompositions and the gases in the foamed adhesives.

For a foamed adhesive to maintain bulk adhesive properties that areeffective for use of dressings of the present invention in the intendedapplications, and to maintain sufficient adhesive properties, the foamedadhesive needs to be prepared with the appropriate degree of foaming.The degree of foaming, i.e. the proportion of gas, e.g. volume,dispersed in and distributed throughout the adhesive composition iseffective to provide the adhesive layer the requisite adhesiveproperties. The degree of foaming in foamed adhesive compositions usedin dressings according to the present invention may be from about 15% to70%, by volume, or from about 20% to about 60% by volume, or about 20%to 40% by volume. The density of foamed adhesive compositions used indressings of the present invention may range from about 0.14 to 0.80g/cm³, or from about 0.19 to about 0.55 g/cm³, or from about 0.19 toabout 0.38 g/cm³.

The foamed adhesives are prepared at the temperature just above thesoftening points of the adhesive material. The temperature may rangefrom about 275° F. to about 375° F., or from about 300° F. to about 315°F. Typically, the processing temperature of the foamed adhesives to beused in dressings for use in wound care ranges from about 325° F. toabout 350° F., and the temperature is slightly lower for foamedadhesives to be used in dressings for use in sanitary protection. Themixing is conducted at a relatively high speed. In addition totemperature and speed of mixing, other conditions of preparing theclosed-cell foamed adhesive compositions must be effective to providethe closed-cell structures substantially homogeneously dispersedtherein.

In order to prepare foamed adhesives with predominately closed cells, asdescribed above, a particularly suitable process for producing thefoamed adhesives is employed as described herein. In this process, thepressure sensitive adhesive is first melted at a temperature greaterthan the melting point of the adhesive, then mixed with dry inert gases,such as nitrogen, air or carbon dioxide, in different proportions byvolume, e.g. 10-80%, under high pressures in sequential mixers, eachequipped with single blade. Such sequential mixers are composed of twomixers, the coarse mixer and the fine mixer, which enables theproduction of the closed cells. The gases e.g. N₂, are pumped into themolten adhesive at high pressure, e.g. from about 800 to about 1500 psi,such that the adhesive pressure is approximately 40-100 psi in the firstmixer, where the coarse mixing occurs. Then the pre-mixture of gases andmolten adhesive is subsequently pumped into the second mixer in order tocontinue fine mixing to yield the foamed adhesives with a substantiallyhomogeneous distribution of closed cells. Additional gas optionally maybe added to the second mixer. Additional mixers may be used as required.The external pressure, i.e. the die pressure, is maintained at 300-600psi. The mixing speed varies from equipment to equipment, but it must besufficiently high to yield a substantially homogeneous distribution ofthe closed cells containing the gas in the adhesives. An exemplarymixing speed is about 100 to about 1000 rpm. Further, to maintain theclosed nature of the cell, the viscosity of the molten adhesives shouldbe in the range of 1,000-50,000 cps, at the temperature where the mixingof the gases and molten adhesives occurs to sustain the close cells. Thefoamed adhesive mixture is transferred through insulated (i.e.temperature controlled) pipes to the dispensing station and dispensedthrough a slot die onto the carrier substrate. The slot die can bedesigned to dispense various patterns to the surface of the substrate,whether over the entire or partial area of the substrate.

Carrier substrates used in the invention may be any substrateconventionally used in applications in which the dressings of theinvention may be used. The foamed adhesive is applied to the substratein order to secure the dressing in place in relationship to the surfaceof the body to which the dressing is applied. The carrier substrateswill have a first side and a second side, opposite the first side, towhich the foamed adhesive composition is applied to form the foamedadhesive layer. The adhesive layer may be continuous, i.e. coveringsubstantially the entire area of the second side of the substrate towhich it is applied. The adhesive layer also may be discontinuous, inwhich case the foamed adhesive may be applied in a pattern, or aroundthe periphery of the second side of the substrate, and the like, thushaving adhesive areas and non-adhesive areas. The total adhesive areamust be sufficient to secure the dressing in place.

In the case of adhesive bandages, the second side of the substratehaving the foamed adhesive layer thereon will be placed directly on theskin, securing the bandage directly to the skin. An absorbent pad may beapplied onto the surface of the adhesive layer facing the skin, in whichcase the adhesive layer may serve to adhere the bandage to the skin, aswell as to adhere the absorbent pad to the carrier substrate, e.g. abacking layer conventionally used in adhesive bandage applications.

In the case of a sanitary napkin embodiment, the carrier substrate maybe used in conjunction with other absorbent pads or layers in order toprovide requisite absorption of body fluids. The second side of thecarrier substrate having the foamed adhesive layer applied thereto isthen place in contact with the undergarment or other article of clothingto secure the napkin in place.

The substrates may be made from woven or knitted fabrics, elastic orinelastic materials, plastic films, paper, nonwovens fabrics, foammaterials, or laminates thereof. Polymeric materials that may be used inpreparation of the carrier substrate include, but are not limited to,polyethylene, polyolefinic films, coextruded polyolefinic films,polyurethane film, and PU/PVC foam backing. In certain adhesive bandageembodiments, the carrier substrate may be a smooth surface or aperturedfilm, such as mono- or co-extruded polyolefin films, e.g. polyethyleneor polypropylene, polyurethane or other thin films. Other substratesinclude a coarse, textured surface/topography as with woven or non-wovenflexible fabrics made from, e.g. natural or synthetic fibers such ascotton, rayon, PET, nylon, polyurethane, etc. In embodiments where thedressing is a sanitary napkin, the carrier substrate may be a film, e.g.polyethylene, or a non-woven e.g. polypropylene.

The foamed adhesive compositions having the closed cells distributedthere through are applied to the side of the carrier substrate thatsecures the dressing of the present invention in relationship to thebody. As noted above, the side containing the foamed adhesive layersecures the adhesive bandage to the skin, while the side containing thefoamed adhesive layer secures the sanitary napkins or liner to anarticle of clothing.

As in the foamed adhesive composition, the closed cells distributedthroughout the foamed adhesive layer have a cell dimension that mayrange from about 1 to about 10 micron, or from about 2 to about 5micron. In some embodiments of the invention, the closed cell may beelongate in structure due to application of the foamed adhesivecomposition to the carrier substrate, in which case the cell dimensionmay be length and/or width of the cell. In other embodiments, the closedcell may be ovoid, spherical or circular in structure, in which case thecell dimension may be an average cell diameter. In certain embodimentsthe cell dimension has a maximum of about 10 micron, or in otherembodiments, the cell dimension has a maximum of about 5 micron.

The thickness of the foamed adhesive layer may be from about 20 to about200 micron, or from about 30 to about 100 micron. The ratio of thethickness of the foamed adhesive layer to the average cell dimension maybe from about 0.005 to about 0.50, or from about 0.03 to about 0.1. Thefoamed adhesive layer may have a basis weight ranging from about 20 toabout 150 g/m², or from about 30 to about 100 g/m², or from about 30 toabout 60 g/m². The density of the foamed adhesive layer may be fromabout 0.14 to about 0.80 g/cm³, or from about 0.19 to about 0.55 g/cm³,or from about 0.19 to about 0.38 g/cm³.

In preparation of the adhesive dressings of the present invention, thefoamed adhesive composition as described herein are coated onto the sideof the carrier substrate that will secure the dressing in place inrelation to the body.

Adhesive dressings of the present invention exhibit a number ofadvantages. First, the amount of adhesive required to be used in theadhesive layer is considerably reduced by the presence of the closedcells filled with gases without adversely affecting the adhesionproperties and bulk properties of the adhesive layer. This provides asignificant savings to the manufacturer due to the reduced amount ofadhesive composition actually used. Further, the foamed adhesive layergives the adhesive dressing a soft and smooth feel, providing animproved comfort upon application.

The adhesive dressings typically have a static shear that is about 20%to about 80% of the static shear of an adhesive dressing comprisingsubstantially the same, or the same, carrier substrate, and a layer ofnon-foamed adhesive composition that is substantially similar to thefoamed adhesive composition. In certain embodiments the dressings of theinvention will have a static shear of about 60%, or about 80% of thestatic shear of an adhesive dressing comprising substantially the same,or the same, carrier substrate, and a layer of non-foamed adhesivecomposition that is substantially similar to the foamed adhesivecomposition. The dressings may have a static shear of about 100 minutesor greater, or 300 minutes or greater, or about 500 minutes or greater,or about 1500 minutes or greater, each as determined by methodsreferenced and described herein below with a static load at 500 g. Asset forth in the claims, all static shear values are determined by themethods described in ASTM 6463, at a static load of 500 g.

Example 1

A hot-melt adhesive composition with no foaming was applied to twodifferent carrier substrates, one being a flexible, woven PET fabric(Control C1) and the other a polyolefin film having outer films of PEand a film of PE/acrylic blend disposed between the outer films (ControlC2). Hot-melt adhesive compositions of varying degrees of foaming wereapplied to the same substrates as C1 and C2, respectively. The hot-meltadhesives were applied to the various carrier substrates atapproximately 160° C. The resulting coated substrates, C1, C2, 1A, 1B,1C and 1D, were then tested for 90° Adhesion and static shear utilizingstandard test methods ASTM 3330 F and ASTM 6463, respectively. Resultsare presented below.

Flexible Fabric PE Backing (Sheer) C1 1A 1B C 2 1C 1D Basis Weight(g/m²) 58 40 28 50 38 25 Foaming (Volume %) 0 31 51 24 50 Thickness(mil) 16.5 11.9 12.6 6.0 5.7 5.3 90° Adhesion/Glass 19 17 14 20 10 4(oz/in) 90° Adhesion/Backing 12 7 6 34 16 8 (oz/in) Static Shear (min.)545 308 195 >6000 >6000 >6000 0.75″ × 0.75″ × 500 g (Static Load) StaticShear (min.) 156 98 n/a Backing breaks - 0.75″ × 0.75″ × 750 g unable tomeasure (Static Load)

As the results indicate, the woven fabric having a foamed adhesive layercontaining about 30 and 50% foaming (by volume) exhibited a static shearof 308 and 195 minutes at a static load of 500 g, respectively. Thepolyolefin films with the same adhesive layer exhibited static shearthat were immeasurable.

What is claimed is:
 1. A dressing suitable for topical application tothe body, comprising: a carrier substrate having a first side andopposing second side; and a layer of a foamed adhesive compositionapplied to the second side of the carrier substrate, wherein the layerof foamed adhesive composition comprises a substantially homogeneousdistribution of closed cells comprising an inert gas contained therein.2. The dressing of claim 1 wherein the closed cells are ovoid,spherical, circular or elongate in structure.
 3. The dressing of claim 1wherein the closed cell comprises a cell dimension selected from thegroup consisting of average diameter, length and width.
 4. The dressingof claim 3 wherein the cell dimension is from about 1 to about 10micron.
 5. The dressing of claim 3 wherein the cell dimension is fromabout 2 to about 5 micron.
 6. The dressing of claim 1 wherein the layerof the foamed adhesive composition has a thickness from about 20 toabout 200 micron.
 7. The dressing of claim 1 wherein the layer of thefoamed adhesive composition has a thickness from about 30 to about 100micron.
 8. The dressing of claim 1 wherein a ratio of the thickness ofthe layer of the foamed adhesive composition to the cell dimension isfrom about 0.005 to about 0.50.
 9. The dressing of claim 1, wherein aratio of the thickness of the layer of the foamed adhesive compositionto the average cell diameter is from about 0.03 to about 0.1.
 10. Thedressing of claim 1, wherein the foamed adhesive composition has adensity from about 0.14 to about 0.80 g/cm³.
 11. The dressing of claim1, wherein the foamed adhesive composition has a density from about 0.19to about 0.55 g/cm³.
 12. The dressing of claim 1 wherein the Inert gasis selected from the group consisting of nitrogen, carbon dioxide, noblegases, hydrocarbons and air.
 13. The dressing of claim 1 wherein thelayer of foamed adhesive composition comprises from about 15% to about70% by volume of the inert gas.
 14. The dressing of claim 1 wherein thelayer of foamed adhesive composition comprises from about 20% to about60% by volume of the inert gas.
 15. The dressing of claim 1 wherein thelayer of foamed adhesive composition comprises from about 20% to about40% by volume of the inert gas.
 16. The dressing of claim 1 having astatic shear of about 100 minutes or more.
 17. The dressing of claim 1having a static shear of about 300 minutes or more.
 18. The adhesivedressing of claim 1 having a static shear of about 1500 minutes or more.19. The dressing of claim 1 having a static shear of about 20% to about80% of the static shear of an adhesive dressing comprising the carriersubstrate and a layer of non-foamed adhesive composition, wherein thenon-foamed adhesive composition is substantially similar to the foamedadhesive composition.
 20. The dressing of claim 1 having a static shearof about 60% to about 80% of the static shear of an adhesive dressingcomprising the carrier substrate and a layer of non-foamed adhesivecomposition, wherein the non-foamed adhesive composition issubstantially similar to the foamed adhesive composition.
 21. Thedressing of claim 1 wherein the adhesive layer has a basis weight offrom about 20 to about 150 g/m2.
 22. The dressing of claim 1 wherein theadhesive layer has a basis weight of from about 30 to about 100 g/m2.23. The dressing of claim 1 wherein the adhesive layer has a basisweight of from about 30 to about 60 g/m2.
 24. The dressing of claim 1wherein the closed cells comprise about 90% or more of the total numberof cells in the adhesive layer.
 25. The dressing of claim 1 wherein theclosed cells comprise about 95% or more of the total number of cells inthe adhesive layer.